A gas turbine engine may be used to power various types of vehicles and systems. A particular type of gas turbine engine that may be used to power aircraft is a turbofan gas turbine engine. A turbofan gas turbine engine conventionally includes, for example, five major sections: a fan section, a compressor section, a combustor section, a turbine section, and an exhaust section. The fan section is typically positioned at the front, or “inlet” section of the engine, and includes a fan that induces air from the surrounding environment into the engine and accelerates a fraction of this air toward the compressor section. The remaining fraction of air induced into the fan section is accelerated into and through a bypass plenum and out the exhaust section.
The compressor section raises the pressure of the air it receives from the fan section, and the resulting compressed air then enters the combustor section, where a ring of fuel nozzles injects a steady stream of fuel into a combustion chamber formed between inner and outer liners. The fuel and air mixture is ignited to form combustion gases.
Known combustors include inner and outer liners that define an annular combustion chamber in which the fuel and air mixtures are combusted. The inner and outer liners are spaced radially inwardly from a combustor casing such that inner and outer passageways are defined between the respective inner and outer liners and the combustor casing. Fuel igniters extend through the combustor casing and the outer passageway, and are coupled to the outer liner by igniter support assemblies attached to the combustor liner. More specifically, the fuel igniter support assemblies secure and maintain the igniters in alignment relative to the combustion chamber as well as provide a sealing interface for the igniter between the outer passageway and the combustion chamber.
During operation, a portion of the airflow entering the combustor is channeled through the combustor outer passageway for attempting to cool the outer liner and igniters and diluting a main combustion zone within the combustion chamber. However, over time, continued operation may induce potentially damaging thermal stresses into the combustor that exceed the strength of materials used in fabricating the components of the combustor. For example, thermally induced transient and steady state stresses may cause low cycle fatigue (LCF) failure of the igniter.
Cooling the igniter, particularly the tip portion of the igniter closest to the combustion process, frequently presents challenges. Some conventional igniters include a plurality of longitudinal slots extending down the length of the igniter to channel cooling air to the vicinity of the tip portion of the igniter. However, this arrangement is generally not very efficient because it typically requires a relatively large amount of cooling air to sufficiently cool the tip portion of the igniter. The large amount of air used to effectively cool the tip portion of the igniter in this manner may adversely impact the combustion conditions within the combustion chamber. Particularly, a large amount of cooling air may have a perturbative effect on the ignition process, gaseous emissions, and the temperature distribution of hot gases entering the turbine. In some arrangements, the quantity and manner in which cooling air is admitted into the combustor may result in a barrier formed around the igniter that prevents fuel from reaching the tip portion of the igniter. This can additionally reduce the effectiveness of the igniter for igniting the fuel and air mixture. Moreover, excess cooling air can disrupt the liner cooling film and result in local hot spots immediately downstream of the igniter in the combustor liner.
In a dual walled combustor, the challenges involved in cooling the igniter are exacerbated. For example, the respective walls and other components may move relative to one another during operation, which should be considered by a combustor designer. Moreover, additional walls require additional sealing arrangements and more complicated paths for the cooling air to reach the igniter tip.
Accordingly, it is desirable to provide combustors with igniters that are efficiently cooled without adversely interfering with the combustion of the air and fuel mixtures in the combustion chamber. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention.